Multi junction APS with dual simultaneous integration

Abstract

A new kind of pixel is formed of two floating diffusions of different sizes and different conductivity type. The two floating diffusions have different image characteristics, and hence form a knee-shaped slope.

1. A pixel cell, comprising:
 a substrate; 
 a semiconductor well, formed in said substrate; 
 a plurality of floating diffusion regions each in contact with said semiconductor well; and 
 a plurality of output transistors each having a gate coupled to a respective one of said plurality of floating diffusion regions. 
 
   
   
     2. The pixel cell of  claim 1 , wherein each of said plurality of floating diffusion regions is formed at a surface of the semiconductor well. 
   
   
     3. The pixel cell of  claim 1 , further comprising:
 an active oxide covering a surface of said semiconductor well. 
 
   
   
     4. The pixel cell of  claim 1 , wherein each of said floating diffusion regions is coupled to a respective reset transistor for supplying a reset voltage in response to a reset signal. 
   
   
     5. The pixel cell of  claim 1 , wherein said semiconductor substrate is of a first conductivity type and said semiconductor well is of a second conductivity type different from said first conductivity type. 
   
   
     6. An image sensor, comprising:
 a semiconductor substrate; 
 a photosensor for supplying photogenerated charge based on light impinging upon said photosensor; 
 a first semiconductor well formed within said semiconductor substrate; 
 a plurality of floating diffusion regions each at least partially formed in said first semiconductor well and for storing photogenerated charge; and 
 a plurality of transistor connection elements operably connected to a respective one of said plurality of floating diffusion regions and for generating signals indicating respective amounts of said photogenerated charge collected by said floating diffusion regions. 
 
   
   
     7. The sensor of  claim 6 , further comprising:
 a plurality of reset elements each for resetting a respective one of said floating diffusion regions. 
 
   
   
     8. The sensor of  claim 6 , wherein said semiconductor substrate is P-type, said semiconductor well is N-type, and said plurality of floating diffusion regions includes at least one N-type region and at least one P-type region. 
   
   
     9. The sensor of  claim 6 , wherein at least one of said floating diffusion regions surrounds another one of said floating diffusion regions. 
   
   
     10. The sensor of  claim 6 , wherein when said sensor is operational said semiconductor well is fully depleted. 
   
   
     11. A method of converting light to a signal, comprising:
 photogenerating charge in response to incoming light; 
 receiving photogenerated charge in a plurality of floating diffusion regions each producing an output indicative of a different gradation of the incoming light; and 
 sampling said charge received by each of said floating diffusion regions using a transistor. 
 
   
   
     12. The method of  claim 11 , wherein each said transistor used to sample a floating diffusion region has a same conductivity type as the floating diffusion region being sampled.